Photographic half-tone screen material and process



Dec. 14, 1937. A. MURRAY 2,102,921

PHOTOGRAPHIC HALF TONE SCREEN MATERIAL AND PROCESS I Filed May 21, 1935 I EMULSION comp/5n TO WWI fifizz zx g mz l0 SUPPORT I /Z LATENT/M1465 OF' ammo HALF-TON: 12075 WIlllllIl/lfl {5 l3 CONT/NUOUS TONE LA TENT (M 5 .7 GRADE 1 5 CONTINUOUS 70857114146:

l4 EMULSION SENSITIVE a 7'0 GREEN LIGHT INVENTOR. I

Alexander M array ATTORNEYS Willllllllfl Patented Dec. '14, 1937 PHOTOGBAPHIC HALF-TONE SCREEN MA-V.

- TERIAL AND rnocnss Alexander Murray, Rochester, N. Y., assignor, by

mesne assignments, to Eastman Kodak Company, Jersey City, N. 1., a corporation oi New Jersey Application May 21, 1935, Serial No. 22,511

90laims.

5 In making half-tone printing plates according to processes in use at the present time, a negative is first made by exposure through a halftone screen g'r he image obtained in this way, whfElT consists of variable-area half-tone dots, is 1 reversed from right to left as required for halftone printing. If the original negative was made on 'a-coiiodion coated glass plate, this may be done by stripping the image from the plate and applying it in a reverse position to another trans l6 parent plate. The photo-mechanical printing plate is then made from this negative by exposinga sensitized metal plate, such as a bichromate-colloid plate under the negative to a strong light, after which the plate is etched. This procau ess requires special apparatus for. making the original negative'and for holding the half-tone screen, and a considerable degree of skill is also necessary to obtain correctly graded half-tone negatives.

It is accordingly an object of the present invention to provide a simpiifledmethod of making half-tone plates. It is a further object to provide a material suitable for making halt-tone screen negatives or positives. Other objects will appear in the following description or my invention.

These objects are accomplished by my invention by the use of a special intermediate element which I shall call a bi-screen transparency", in which a half-tone screen is formed photographically.

In the accompanying drawing Figs. 1-4 represent a modification oi my invention in which an image of half-tone dots and a continuous tone 0 image are formed in a single emulsion layer.

Fig. 5 represents another modification in which the image of half-tone dots and the continuous tone image are formed in separate emulsion layers on opposite sides of a support.

Fig. 6 represents a modification in which the image of half-tone dots and the continuous tone image are in separate emulsion layers on the flcation shown in Figs. 1-4, Fig. 1 is a section view of the material in which the half-tone screen; and continuous tone image are impressed. As shown in this figure, I0 represents a support oi transparent material, such as glass or a cellulosic 5 material, such as cellulose acetate or cellulose nitrate.,., On'this support is coated a layer of sensitive material II which may be a silverhalide gelatin emulsion. The emulsion is prererably colored to absorb apart of the light to 10 which the emulsion is sensitive. In the case of a gelatino-halide emulsion, the emulsion is sensitive to blue light, and the layer is accordingly colored yellow to absorb a part or the blue light. The reason for this will be pointed out later. The sensitive material is first exposed, for example, from the emulsion side to a ruled crossline screen, in order to form a latent image l2 ofthe screen which I will refer to as a-latent image of graded half-tone dots. A single dot, ii magnified, would show a density gradient, or a so-called vignetted eilect. This exposure may be produced by any known means, as by flash exposure with the proper diaphragm opening through a ruled cross-line screen placed at the proper distance irom the emulsion or by exposure through a contact screen or by projection. The material containing the latent image may be used at once to produce a continuous tone image or picture, or it may be stored as a sensitive material containing the latent image oi. graded half-tone dots and may be exposed later to form the continuous tone image. When the continuous tone image is to be formed, the film or plate is exposed to the object through the support I to form the '35 continuous tone latent image l3 in the emulsion layer adjacent the support as shown in Fig. 3. The plate or film is then developed and fixed and the latent images assume the form shown in Fig. 4 in which the image of graded dots is rep- 40 resented at I4 and the continuous tone image at l5.

The images of the graded dots' and of the picture, or the continuous tone image, do-not meet in the emulsion layer, as may be seen in the drawing. This separation of the individual images is necessary in order that one of the images does not overlap or destroy the other image. This condition is attained by coloring the emulsion layer a color which absorbs the light to which the emulsion is sensitive. The light which ailects the emulsion can therefore penetrate only a short distance into the emulsion layer, and it is prevented from passing into the emulsion layer to such a distance that the image on the opposite side of the emulsion layer is affected. The dye or coloring matter which is used in the emulsion layer is of such a nature that it is removed in the processing baths, suchas the developing or fixing baths.

In the modification of my invention illustrated in Fig. 5. a support Ilia of transparent material is colored so that it absorbs a part or all of the light to which the emulsion layers which it carries are sensitive. Thus, the emulsion layers i I coated on both sides of the support may be of the same type, that is, silver-halide emulsions sensitiveto blue light. In this case the support Hla would be colored a deep yellow to absorb the blue light. The image of graded dots and the continuous tone image l5 are formed as before, by exposure of the plate or film from opposite sides. In this case, however, less care need be exercised to insure the images being recorded only to the proper depth, since the deeper color of the support is more likely to prevent exposure of the emulsion layer on the opposite side of the support.

It is to be understood, however, that, while I have described the material used in my process as being colored, this feature is not absolutely necessary. The emulsion or support may be uncolored, and the exposure regulated so that the images of the screen and the object are kept separate. In the modification about to be described, another method is employed which makes coloring of the material unnecessary.

In the modification of my invention illustrated in Fig. 6, the support In is coated on one side with two emulsion layers 16 and I! which are sensitive to light of different colors. For example, the emulsion layer l6 may be sensitized to red light by any known means, and the emulsion layer i1 sensitized to green light. The image I of the graded half-tone dots is formed by exposure through a green filter which does not affect the layer IS. The continuous tone image is then formed by exposure through a red filter which records only in emulsion layer l6 which is sensitive to red light.

The modification illustrated in Fig. 7 is similar to that illustrated in Fig. 4, but the screen image It is made by exposure through the support, and therefore is recorded in the emulsion layer adjacent the support. The continuous tone image I5 is made by exposure from the surface of the emulsion layer, and lies in the emulsion layer adjacent the outer surface. When the screen negative is made from this bi-screen positive, as described below, the dot structure shows a sharper outline than with the type of positive illustrated in Fig. 4. However, satisfactory dot structure may be obtained with the type of positive shown in Fig. 4, by placing a sheet of clear film between the biscreen positive and the emulsion of the screen negative, and printing with the emulsion of the positive toward the emulsion of the negative.

The following specific example will illustrate a method of forming a bi-screen transparency, such as that illustrated in Fig. 7.

A sensitive film material consisting of a yellow dyed, low gamma emulsion coated on uncolored nitrate film base is exposed from the support side for ninety seconds under a 65-line half-tone screen placed at a distance of kg of an inch from the emulsion. The exposure is made through a ten-inch lens placed twenty inches from the film with a diaphragm opening of F/45. The screen is illuminated with a 500 watt tungsten lamp, placed 1 foot from the lens, with ground glass diffusers between lens and lamp.

Water oz 16 p-Methylaminophenol sulfate grains 14 Sodium sulphite, desiccated oz 2 Hydroquinone grains Sodium carbonate, desiccated do 360 Potassium bromide do 70 Water to make oz 32 The resulting positive which I have referred to as a bi-screen transparency, is'then exposed in a high pressure printing frame to a high gamma emulsion film with the support in contact with the film. for twelve seconds under a l50-watt tungsten lamp, placed four and one-half feet away. The exposure may be varied, as required, so that the light from the exposure lamp passes through the continuous tone image sufficiently to produce a shadow dot on the high gamma emulsion film at the densest portions of the continuous tone image. It is thus reversed from right to left, as required for photo-engraving. The high gamma film is then developed at 65 F. for two minutes in a developer having the following formula, after which it is fixed, washed, and dried:

Water oz 64 Sodium sulfite oz 4 Trioxymethylene oz 1 Potassium metabisulfite grains Boric acid oz 1 Hydroquinone oz 3 Potassium bromide grains 90 Water to make gal 1 The photo-mechanical screen negative result? ing from this process has a full scale dot formation extending from shadow to highlight, and is equivalent in detail to the best photo-mechanical screen negatives at present obtainable.

I have described my invention as being applied to the production of a bi-screen transparency which contains positive image, from which a screen negative must be made for producing the half-tone printing plate. According to this process, the sensitive material is exposed to an ordinary negative after the exposure under the halftone screen, in order to form the bi-screen positive. Since the exposure of the final negative is made through the support, the screen negative has the image reversed from right to left, and the photo-mechanical printing plate may be made directly from it. It is to be understood, however, that I am not limited to this manner of procedure. The bi-screen transparency made according to my invention may be either a positive or a negative. For example, the continuous tone or picture image may be formed on the bi-screen material by exposing it directly to the object to be photographed, and a bi-screen negative obtained at once. This negative may then be printed directly on metal sensitized with a high gamma emulsion, which is then etched to form a photobi-screen transparencies, either negative or positive, may be made according to my invention in any camera equipped to take plates or films, or in an enlarger, or in a printing frame. For this reason, special equipment, such as half-tone screen supports and plate holders, may be dispensed with. The emulsion used to record the bi-screen image is of relatively low gamma or contrast, consequently, much faster emulsions are available than have previously been used with half-tone materials. The resolution of detail is also found to be better than in present screen processes.

A further advantage of my process is that it simplifies allowing for variations in contrast in different originals. In the present halftone camera process, great skill is required in manipulating diaphragm stops to adapt optical conditions to the individual contrast range of each original to be reproduced. With bi-screen film, these contrast variations are compensated by varying the continuous tone image, or picture, exposure time. To increase the contrast of the resulting screen negative, the above-mentioned exposure time is simply increased, and vice versa.

It is to be understood that I am not limited to the modifications referred to in the above description of my invention but that I contemplate all equivalents coming within the terms of the appended claims.

What I claim is:

1. A process for making a half-tone screen transparency from an element comprising a transparent support having thereon a lightsensitive silver halide emulsion layer containing a dye of a color complementary to the color to which the emulsion is mainly sensitive, which comprises exposing the emulsion under a uniformly illuminated half-tone screen to form a latent image of the screen on one surface of the emulsion, exposing the emulsion from the opposite side to an object to be photographed to form a continuous tone latent image of the object in a separate stratum of the emulsion, and developing and fixing both latent images to form separate visible images .in the element.

2. A process for making a half-tone screen transparency from an element comprising a support having light-sensitive silver halide emulsion layers on opposite sides thereof, the element con taining a dye of a color complementary to the color to which at least one of the emulsion layers is mainly sensitive, which comprises exposing one of the emulsion layers under a uniformly illuminated half-tone screen to form a latent image of the screen in that emulsion layer, exposing the other emulsion layer to an object to be photographed to form a continuous tone latent image of the object in the second emulsion layer, and

sion layers each sensitive to light of a diiferent color on one side of said support, and a half-tone screen latent image of a uniform light source in one of the emulsion layers.

5. A single photographic element comprising a support having thereon a developed and fixed half-tone screen image of a uniform light source, and a distinctly separate developed and fixed continuous tone image of a subject in a transversely-spaced portion of the element.

6. A photographic element comprising a support, an emulsion layer on said support, a developed and fixed half-tone screen image of a uniform-light source in one stratum of the emulsion layer, and a developed and fixed continuous tone image of a subject in a separate stratum of the emulsion layer.

7. A photographic element comprising a support, an emulsion layer on each side of said support, a developedand fixed-half-tone screen image of a uniform light source in one emulsion layer and a developed and fixed continuous-tone image of a subject in the other emulsion layer.

8. A photographic element comprising a support, at least two emulsion layers on one side of said support, a developed and fixed half-tone screen image of a uniform light source in one emulsion layer and a developed and fixed continuous-tone image of a subject in the other emulsion layer.

9. A photographic element comprising a transparent support, light sensitive silver halide emulsion in layer form thereon, a readily removable light restraining dye in the element tending to prevent penetration of light through the element, and a latent screen image in only one stratum of the emulsion, the screen image comprising dots and having uniform characteristics over the whole area of the element, the element being otherwise unexposed, whereby there is left an unexposed sensitive stratum capable of having an image printed therein.

ALEXANDER MURRAY. 

